Without limiting the scope of the invention, its background is described in connection with the photocatalytic conversion of methane to methanol. Methane, a major component of natural gas, is an abundant material world-wide; however, it is difficult and costly to transport as a gas. The conversion of methane to a more easily transported source (e.g., methanol) is important in many industries including the oil and gas industry. In addition, methanol is a key building block to many valuable chemical products. Production of alcohols by oxidation has been difficult because the oxidation reaction tends to completion to carbon dioxide and over-oxidation is a persistent problem. Therefore, conventional approaches to synthesize methanol from methane generally have poor conversion efficiencies, slow reaction rates, and requires abundant energy sources, making them impractical.
For example, U.S. Pat. No. 8,211,825, entitled, “Methanol Oxidation Catalyst,” discloses a methanol oxidation catalyst comprising a material of composition: PtxMzTau in which Pt is platinum, Ta is tantalum, M is an element which comprises at least one selected from the group consisting of V (vanadium), W (tungsten), Ni (nickel) and Mo (molybdenum), x is 40 to 98%, z is 1.5 to 55%, and u is 0.5 to 40%. To maximize catalytic activity the material is preferably in the form of nanoparticles. The values of x, z, and u are selected such that the element exhibits X-ray photoelectron spectroscopy peaks derived from an oxygen bond and a metal bond in which a peak area derived from the oxygen bond is twice or less the peak area derived from the metal bond.
For example, U.S. Pat. No. 8,173,851, entitled, “Processes for Converting Gaseous Alkanes to Liquid Hydrocarbons,” discloses a process for converting gaseous alkanes to olefins, higher molecular weight hydrocarbons or mixtures thereof wherein a gaseous feed containing alkanes is thermally reacted with a dry bromine vapor to form alkyl bromides and hydrogen bromide. Poly-brominated alkanes present in the alkyl bromides are further reacted with methane over a suitable catalyst to form monobrominated species. The mixture of alkyl bromides and hydrogen bromide is then reacted over a suitable catalyst at a temperature sufficient to form olefins, higher molecular weight hydrocarbons or mixtures thereof and hydrogen bromide. Various methods are disclosed to remove the hydrogen bromide from the higher molecular weight hydrocarbons, to generate bromine from the hydrogen bromide for use in the process, and to selectively form mono-brominated alkanes in the bromination step.
For example, U.S. Pat. No. 6,156,211, entitled, “Enhanced Photocatalytic Conversion of Methane to Methanol Using a Porous Semiconductor Membrane,” discloses a method and apparatus for the conversion of methane in solution or gas which provides a photochemical conversion in a unique two-phase boundary system formed in each pore of a semiconductor membrane in a photocatalytic reactor. In a three-phase system, gaseous oxidant, methane contained in a liquid, and solid semiconductor photocatalyst having a metal catalyst disposed thereon, meet and engage in an efficient conversion reaction. The porous membrane has pores which have a region wherein the meniscus of the liquid varies from the molecular diameter of water to that of a capillary tube resulting in a diffusion layer that is several orders of magnitude smaller than the closest known reactors.
For example, U.S. Pat. No. 5,720,858, entitled, “Method for the Photocatalytic Conversion of Methane,” discloses a method for converting methane to methanol which involves subjecting the methane to visible light in the presence of a catalyst and an electron transfer agent. Another embodiment of the invention provides for a method for reacting methane and water to produce methanol and hydrogen comprising preparing a fluid containing methane, an electron transfer agent and a photolysis catalyst, and subjecting said fluid to visible light for an effective period of time.
For example, U.S. Pat. No. 6,137,017, entitled, “Methanol Process for Natural Gas Conversion,” discloses a process for producing methyl alcohol from natural gas using chlorination technology. The process includes reacting methyl chloride, hydrogen chloride, oxygen and perchloroethylene in a catalytic reactor to give methanol product and hexachloroethane and using the C2C16 to chlorinate methane of natural gas feedstock in multiple thermal chlorination reactors, each with a natural gas recycle loop. These reactors are arranged in a cross-flow reactor system whereby a gas purge from the first reactor is fed to the second, and so on if necessary until a last reactor, which is vented to the atmosphere by feeding a purge steam to the catalytic reactor.